In order to understand the mechanism of insulin action, numerous insulin-like agents have been studied with hormone-responsive cells such as the isolated rat adipocyte. Sulfhydryl oxidizing agents and concanavalin A stimulate D-glucose uptake by rat cells, as do antibodies against rat adipocyte membrane proteins. Interestingly, monovalent Fab fragments of these anti-membrane antibodies fail to elicit the response in target cells observed when intact antibodies are used. These recent findings suggest that a multivalent aggregation or capping of some kind may play a key role in producing this insulin-like action on target cells. The proposed research investigation would utilize my previous experience with the production and use of anti-membrane antibodies to address more directly the question of how these antibodies mimic insulin action. Considerable use would be made of experiments involving concanavalin A, another multivalent reagent capable of mimicking insulin action. Among the questions to be addressed are the following: a) Are the effects of concanavalin A and the anti-membrane antibodies identical to those of insulin on all metabolic activities studied? (Any differences might reflect pathways which are not activated by an intermediate step involving aggregation of a membrane protein). b) Do the antibodies and convanavalin A interact with the same membrane protein(s)? (Recent data suggests that the antibodies bind to a 94,000 dalton glycoprotein). c) Is the rat adipocyte 94,000 dalton glycoprotein unique, or would antibodies against any rat adipocyte glycoprotein mimic insulin action? d) Would Fab fragments bound to the 94,000 dalton glycoprotein interfere with concanavalin A action? with insulin action? e) Do antibodies give a "fossil effect"? i.e. do they cause some stable change in the cell surface which is retained after cellular disruption and the purification of plasma membranes? The answers to these and other related questions are clearly obtainable and they can provide us with an important insight into the basic mechanism of insulin action.